Current status of the known populations of Lejeunea mandonii in ...

2
Article
As part of his British Trust for
Conservation Volunteers (BTCV)
Natural Talent Apprenticeship, Oliver
Moore was asked to undertake a
search for Lejeunea mandonii at a
John Muir Trust reserve along the
Drinan coast, Strathaird, Isle of Skye.
The project eventually expanded to
include all known sites for this species
in Scotland. It is hoped that this
report will stimulate efforts to find new
records of this liverwort.
Current
status of
the known
populations
of Lejeunea
mandonii in
Scotland
FieldBryology No103 | Feb11
Lejeunea mandonii (Steph.) Mull.
Frib. (Atlantic pouncewort) (Fig. 1)
is listed in the Red Data Book as
endangered and is a rare plant worldwide,
occurring on the Atlantic fringe
of Europe, in Britain, Ireland, Spain and Portu-
gal, and also in Macaronesia (Church et al.,
2001). Consequently, the British populations of
this liverwort are of international importance and
it is a Biodiversity Action Plan priority species.
L. mandonii was first found by Dr Symers
Macvicar at Invermoidart in 1898. It is
frequently found with other hepatics such as
Frullania spp. and Radula spp. (Hill et al., 1991),
as well as mosses such as Neckera complanata
and Zygodon spp. in lightly shaded situations.
L. mandonii occurs by the coast, near sea level,
in its Scottish and English localities, and here
it grows in relatively dry places where there is
constant humidity (Rothero, 2002). L. mandonii
is a southern Atlantic liverwort according to
Ratcliffe (1968) and its northernmost locality in
the world occurs on the Isle of Skye (Fig. 2).
Surveys of the five recorded Scottish sites in
1996 and 2000 found the plant on just three
individual ash (Fraxinus excelsior) trees. These
were in fairly open ravines of calcareous rock,
with a southerly or westerly aspect, where the
humidity remained high, but where there was
still a reasonable amount of insolation (Rothero,
2002). Rothero (2002) conducted a very
thorough search of similar habitats at Moidart
in ravines parallel to those where the species had
been found, but without success.
At Laudale, Rothero (2002) was following
up a vaguely located record from 1967, made
Lejeunea mandonii in Scotland
by John Birks, from Meall a’ Chuilinn. Most of
the stands of Lejeunea spp. were rejected in the
field and collections of small Lejeuneaceae from
calcareous rock here proved to be small forms of
L. patens. The author also noted that the ravines
at Laudale were very different from those at
Moidart, but a small population of L. mandonii
would be easily overlooked amid the abundant
L. patens.
The present survey set out to monitor the
status of the three existing populations of L.
mandonii in Scotland and to search the Drinan
coast thoroughly in another attempt to refind the
locality reported by Birks & Birks (1974).
According to Paton (1999), well-developed
populations of L. mandonii can be recognized in
the field vegetatively by the consistently narrow
shoots and the rather narrowly rounded apex of
b Fig. 1. L. mandonii. F. Rumsey.
b Fig. 2. 10 km distribution of
L. mandonii in Great Britain and
Ireland. j, 2000–2010 records;
j, 1959–1999 records. Map taken
from the NBN gateway using data
from the BBS and BRC. © Crown
Copyright. All rights reserved
NERC 100017897 2004
FieldBryology No103 | Feb11 3

More acute apex to leaf
lobes (but sometimes folded
below) and narrow shoots
More acute angle
many of the leaves. L. mandonii is the only British
member of the genus that has terete, smooth
perianths, but these may be very small and are
then not always easily located in the field (Paton,
1999). Capsules are reported as being very rare,
occurring in the spring (Holyoak, 2004), and
perianths are occasional (Smith, 1990). There
is no specialized means of vegetative spread
(Rothero, 2002).
Confusion species in the field include L. patens
and Harpalejeunea molleri, both of which may
grow with L. mandonii, making things very difficult
(Rothero, 2002). H. molleri differs in its
underleaves and more acute leaf lobes, while in
L. patens the angle between the postical margin
and the keel is narrower (Paton, 1999). L. patens
has a more broadly rounded leaf apex compared
to its rarer congener. Fig. 3 illustrates some of
the differences between the species mentioned
above. It should be added that shaded stems of L.
lamacerina, L. patens and L. cavifolia can produce
leaves that are longer than usual (Holyoak, 2004)
and when occurring on small specimens of these
species, distinguishing them from L. mandonii is
even more difficult.
Broadly rounded apex to
leaf lobes and usually larger
shoots
Narrowly rounded apex
to leaf lobes and narrow
shoots
m Fig. 3. Illustrations of some possible confusion species. From left to right: H. molleri, L. lamacerina, L. patens and
L. mandonii. Postical view (upper row) and antical view (lower row). Magnification x40. O. Moore
Procedure
Herbarium specimens of L. mandonii, L.
cavifolia, L. lamacerina, L. patens, H. molleri and
Drepanolejeunea hamatifolia were scrutinized
at the Royal Botanic Garden, Edinburgh, in
preparation for field work. In order to become
acquainted with the target liverwort in the
field, a site visit to one of its known locations at
Tokavaig was undertaken on 27 February 2010.
On 1 March 2010, Nick Hodgetts joined me in
the field on a spectacular day to begin the search
for this elusive liverwort in sea caves along the
Drinan coast (Fig. 4). A few days before, by
means of an open canoe, a 3-km stretch of coast
had been viewed to see which sea caves showed
the greatest potential to search in.
According to Birks & Birks (1974), L. mandonii
was said to be very rare (on Skye), restricted to
a single locality in the Elgol Peninsula where
it occurs with Marchesinia mackaii on dry but
shaded Jurassic limestone rocks in a large sea cave.
Rothero (2002) tracked down Birks’ notes from
his original discovery and was able to add ‘…
somewhere between grid reference 18/553 160 and
18/548 147’. During the search, a vast amount
m Fig. 4. Drinan coast with view north to the Red Cuillins.
O. Moore
of M. mackaii was examined, and every smallleaved
patch of L. patens was studied carefully.
A small amount of material was collected for
checking with a microscope.
During the next couple of weeks, visits were
made to different coastal gullies, sea caves and
wooded ravines along this stretch of coast, and
beyond the area specified by Birks & Birks
(1974).
On 5, 19 and 20 March 2010, visits were
made to the known locations for L. mandonii at
Tokavaig (Skye), Allt Ailein and Allt a’ Mhuillin
(Moidart), respectively. At each site the distribution
of the liverwort was mapped onto a sketch
of the relevant facies of the tree. An estimate of
the area of each patch, or extent of the scattered
shoots, was made using a transparent overlay with
1 cm grid squares marked on. The total area on
each tree was calculated by adding up all of these
values (Table 1). Accurate grid references were
determined with a GPS device and photographs
of the trees and habitat were taken for future
reference. A search of other suitable habitat in
each of these ravines was made to try and find
other populations of L. mandonii. A bad weather
forecast limited my search to just one other
adjacent ravine (Limekiln Burn) at Moidart.
Observations
Fig. 5 gives a crude idea of the extent of L.
mandonii populations at its known localities in
Scotland. More accurate and detailed mapping
of the distribution of this species onto sketches of
Table 1. Total area of patches and/or scattered shoots of L. mandonii on different aspects of the three ash trees
on which it occurs in Scotland
Date Location Area (cm 2 ) of patches/scattered shoots on tree-faces
N-facing NE-facing W-facing S-facing
5/3/10 Tokavaig 210 – 21 12
19/3/10 Allt Ailein 208 28 – –
20/3/10 Allt a’ Mhuillin – 18 – –
4 FieldBryology No103 | Feb11 FieldBryology No103 | Feb11 5

(a)
Table 2. Total area of L. mandonii from the three ash trees on which it occurs in
Scotland in 2010 compared with that estimated by Rothero (2002) in 2000
Location Estimated total area (cm 2 ) of scattered shoots/patches of
L. mandonii
2000 2010
Tokavaig Approx. 150 233
Allt Ailein Might approach 600 236
Allt a’ Mhuillin Not more than 30 18
(b)
(c)
b Fig. 5. Distribution of L. mandonii on some of the
ash trees observed in this study. (a) North-facing
side (Tokavaig, lower trunk); (b) north-east face (Allt
a’ Mhuillin); (c) north-face (Allt Ailein, lower trunk).
O. Moore
the trees gave the total estimated areas as shown
in Tables 1 and 2. Table 2 also includes the areas
estimated by Rothero (2002). Despite a great
deal of effort, L. mandonii was not found along
the Drinan coast or in potential locations further
south. No new populations were discovered in
Allt Ailein, Allt a’ Mhuillin or Limekiln Burn.
Conclusions
Rothero (2002) points out that L. mandonii was
intimately mixed with other Lejeuneaceae at the
Scottish sites, making accurate assessments of
population size difficult without much damage
to the stands. No specimens were collected
from the known populations in this survey and
estimates of population size were entirely the
result of close scrutiny of the epiphytes in situ.
The main disparity between the total area of
L. mandonii estimated in the present survey and
that of Rothero (2002) occurred at Allt Ailein,
with nearly three times less measured in 2010.
However, patches of L. mandonii still occur over
some 2 m of the tree trunk (Fig. 5c) as they did in
the 2000 survey. Rothero (2002) concedes that it
was just possible that some of the stands recorded
were small forms of L. patens, but this could not
be investigated without an unwarranted level of
collection. In the present survey, these stands
might well have been taken for the commoner
species, resulting in a lower estimate of cover for
L. mandonii.
Holyoak (2000) suggested that there might
be a relationship between the vigour and growth
of L. mandonii and the growth, persistence
and decay of the mosses on which it usually
grows. Therefore, the year to year variation in
abundance could be a natural phenomenon
and not a cause for concern. This went with
the proviso that further investigation would
be needed to test this hypothesis. Anecdotal
evidence in support of this suggestion comes
with the observation that the population of L.
mandonii on the ash tree at Tokavaig appears to
have moved around quite a bit over the years
(N. Hodgetts, pers. comm.). Some evidence of
sloughed bryophyte cover was observed at this
site and it is possible that some of the patches
recorded by Rothero (2002) had been lost as a
result. L. mandonii is a brittle plant and it may
well be susceptible to damage from raindrops or
moving water (Holyoak, 2004), so a powerful
rainfall event may have caused a loss to the
population in the last 10 years. There were fewer
patches found down the north-east aspect of the
tree at Allt Ailein compared to 10 years previously
(Rothero, 2002); this may have been due to a
storm event. Following annual repetition of the
measurements of patches from 1997 to 2003/4
at Cornish localities for L. mandonii, there
were erratic fluctuations at most sites (Holyoak,
2004). Maybe a similar fluctuation is occurring
in the Allt Ailein population.
There appears to have been an increase in cover
of L. mandonii at Tokavaig and a decrease at Allt
a’ Mhuillin. The bulk of the populations of L.
mandonii in Scotland occur on the north/north-
Lejeunea mandonii in Scotland
east-facing aspects of ash trunks (Table 1). The
best patches were found beneath branches on the
trunk. Holyoak (2004) suggests that limitation
to these places may be due to avoidance of
competition from the vigorous growth of pleurocarpous
mosses. Since L. mandonii obtains
all of its water from humid air, this must be
characteristic of the sites where it occurs. The
aspects where it occurs, however, would generally
confer drier and more shaded conditions for this
liverwort.
The fact that L. mandonii is only known from
just three ash trees makes this species extremely
threatened in Scotland. Rothero (2002) expressed
his concerns about the ivy on the ash at
Tokavaig and this could yet become a problem,
but at present the L. mandonii population
appears to be doing well here. Competition from
more robust bryophytes was a concern at Allt
a’ Mhuillin (Rothero, 2002) where the L.
mandonii population is very small. This population
does appear to have declined. At Allt
Ailein, Rothero (2002) commented on the
rather sorry-looking ash tree that holds a good
population of L. mandonii. The tree still remains
in 2010. Rhododendron ponticum was not seen in
the vicinity of any of the three sites, but it does
occur to the east of Allt a’ Mhuillin. At present
there is no immediate risk of shading by this
species.
All three trees are close to a stream edge in
steep-sided, rocky ravines and may be prone to
an extreme rainfall event causing bank collapse
or large debris being washed downstream. Such
an event could be catastrophic to any species with
so restricted a population. Rothero (2002) urged
research into the ex situ cultivation of L. mandonii,
with a view to transplantation into a suitable
habitat. This proactive measure might ensure the
survival of this liverwort at the northern limits
of its range. More regular monitoring of these
6 FieldBryology No103 | Feb11 FieldBryology No103 | Feb11 7

Lejeunea mandonii in Scotland
populations is recommended so that decisions
concerning conservation strategy can be made
quickly in the event of disaster.
During the preparation of this report, Birks’
herbarium arrived at the RBGE and contained
two specimens of L. mandonii, both from the
Drinan coast, Skye. Each had been refereed
successfully. One specimen was collected on 2
July 1967 and the other on 9 August 1968. In
each case it had been growing with M. mackaii
and the latter collection was from a shaded sea
inlet near Kilmarie. However, there was no
accurate grid reference. Even after considerable
time spent on unsuccessful searches of the
Drinan coast during this survey and by others
(Rothero, 2002; Averis 1995), it is still possible
a few shoots of this tiny liverwort could have
escaped detection.
Since all of the sites where L. mandonii occurs
have enjoyed relative stability for centuries,
Holyoak (2004) suggests there is a need for
historically stable habitats within the Atlantic
climate zone in order for this liverwort to grow.
Bryologists are urged to keep an eye out for this
rarity whenever they find themselves in humid
ravines with overhanging, basic rocks and old
woodland with ash trees in Scotland.
Oliver Moore
The Stonemans, Letterewe, Achnasheen,
Ross-shire IV22 2HH (e bloaterol@yahoo.com)
Acknowledgements
I wish to thank Liz Auty for inviting me to carry out work for
the John Muir Trust and for her support during my placement.
Thanks also to the John Muir Trust team at the Skye office for
putting up with me for several weeks. I am grateful to Lester
Standen for taking me out on the open canoe to look at the
sea caves at the beginning of this quest. Nick Hodgetts spared
8 FieldBryology No103 | Feb11
time to help with the search along the Drinan coast and gave
useful guidance concerning this report. The encouragement I
received from my mentors, David Long and Liz Kungu from
the RBGE, fired my enthusiasm at the start of this project.
Thanks also to Gordon Rothero for his invaluable advice and
interest. Sally Rae kindly located the L. mandonii specimens
from Birks’ herbarium at the RBGE. This survey would not
have been possible without the financial support of the BTCV
Natural Talent Scheme (through Heritage Lottery Funding). I
was thrilled to receive a John Muir Award (Conserver Level)
with the publication of this article.
References
Averis, B. (1995). A Botanical Survey of the Woods of the Elgol-
Torrin Area, Skye. Unpublished.
Birks, H.J.B. & Birks, H.H. (1974). Studies on the bryophyte
flora and vegetation of the Isle of Skye. I. Journal of Bryology
8, 19–64, 197–254.
Church, J.M., Hodgetts, N.G., Preston, C.D. & Stewart,
N.F. (2001). British Red Data Books. Mosses and Liverworts.
Peterborough: Joint Nature Conservancy Council.
Hill, M.O., Preston, C.D. & Smith, A.J.E. (1991). Atlas of
the Bryophytes of Britain and Ireland, Vol. 1, Liverworts.
Colchester: Harley Books.
Holyoak, D.T. (2000). Atlantic lejeunea (Lejeunea mandonii).
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from the Brink Project/English Nature – Species Recovery
Programme, Report No. 142.
Holyoak, D.T. (2004). Lejeunea mandonii (Steph.) Mull. Frib.
UK Biodiversity Action Plan. www.plantlife.org.uk/uk/
assets/saving-species-dossier/Lejeunea_mandonii_dossier.
pdf
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Colchester: Harley Books.
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bryophytes in the British Isles. New Phytologist 67, 365–439.
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Cambridge: Cambridge University Press.